On this day in 1963, in a speech before the United Nations General Assembly, President John F. Kennedy offered to mount a joint manned lunar program with the Soviet Union. Kennedy’s proposal that the two rival superpowers cooperate on a mission to mount an expedition to the moon caught both the Soviet leadership and many Americans off guard.

Toward the end of his address, Kennedy said: “In a field where the United States and the Soviet Union have a special capacity — space — there is room for new cooperation, for further joint efforts. I include among these possibilities,” he added, “a joint expedition to the moon.”

Why, the president asked, should the United States and the Soviet Union conduct parallel efforts that would include “duplication of research, construction and expenditure?” He suggested a joint series of space missions, which if enacted, he said, “will require a new approach to the Cold War.”

Soviet leader Nikita Khrushchev rejected the proposal. But in 1997, his son, Sergei Khrushchev, told SpaceCast, that some weeks after the Kremlin’s rejection, his father had second thoughts. While Khrushchev agreed with his military brass that such an effort would provide an opportunity for the U.S. military to learn more about Soviet missile programs, he also believed that it might be possible for the Soviets to absorb American technology.

Congress would have had to approve the plan, thereby opening the space program to direct Soviet involvement, a politically unpalatable notion in the 1960s’ Cold War environment.

In the wake of Kennedy’s assassination some two months later, both President Lyndon B. Johnson and Khrushchev abandoned the idea while each nation pushed ahead with its own lunar landing program. In 1969, the U.S. became the first and, so far, the only country to land a man on the moon.